A Novel Electromagnetic Actuator Based on Displacement Amplification Mechanism

This paper introduces a new type of linear actuator using the electromagnetic attractive force, which enables a submillimeter stroke. In general, actuation by the electromagnetic attractive force causes a tradeoff problem between the thrust force and the stroke because the thrust force depends on the gap between the electromagnet and the armature; an increase in the gap (stroke) drastically degrades the thrust force. To realize a submillimeter stroke while retaining a high thrust force, a structure that adopts a displacement amplification mechanism is proposed, which is often used to expand the stroke of a piezoelectric actuator. First, the electromagnetic attractive force is theoretically examined with and without displacement amplification. We verify that displacement amplification could create a higher thrust force and energy efficiency over a certain displacement. On the basis of this examination, a prototype actuator is designed, and the driving principle is illustrated. Further, an analytical model of the proposed actuator is developed for control and performance estimation. Several fundamental experiments with a developed actuator are performed in order to reveal the potential of the proposed actuator. The performance evaluations show that the maximum stroke is approximately 450 μm and a bandwidth greater than 300 Hz can be realized, and more a time constant is approximately 2 ms for a stroke of 450 μm. In addition, the experimental results were compared with the simulation results calculated from the analytical model to verify whether the prototype drives predictably according to the proposed concept under a dynamic situation. These results demonstrate that the proposed actuator enables good actuation performance, and it implies that there are tremendous advantages from the viewpoints of manufacturing, assembly, control, etc.